The invention relates to an active part of an electric machine, wherein the active part comprises at least two teeth which each have a magnetically permeable material and which each protrude from a lateral surface of the active part in the radial direction and at least one winding groove which in each case is arranged between a pair of the at least two teeth, wherein the at least one winding groove is arranged substantially along an axis of rotation of the active part and wherein an electrical winding is able to be arranged in the respective winding groove. The invention further relates to an electric machine having such an active part.
Such an active part is designed, for example, as a rotor of a large electric machine. The cooling of such a rotor generally requires costly cooling systems with flow paths in the vicinity of the heat sources. In particular with non-salient pole machines, the rotor cores being designed to be solid, such as for example in turbomachines, technical and technological limitations are present in the design of the cooling channels. For these reasons, both the cooling surface and the cross-sectional surface for the cooling flows is limited. The close association between the benefit in terms of cooling technology and technical complexity is in turn reflected in high production costs.
Although cooling exclusively over the rotor surface might be associated with a considerably lower production cost, in large machines it is not possible to cool the rotor winding sufficiently. A significant proportion of the total temperature difference between the rotor winding and the cooling medium is based on the long cooling paths through the rotor teeth. The materials able to be used for the rotor core are set by mechanical and magnetic requirements.
The problem, amongst others, therefore, is that the previous solutions are either cost-intensive or insufficiently effective.
Cost-effective cooling of the rotor via the lateral surface thereof was hitherto only able to be implemented in small turbo rotors having a shaft output of less than 5 megawatts. However, then the rotor losses have to be significantly limited, i.e. only low excitation current density values are possible. Thus such cooled rotors have a large diameter or are particularly long. The temperature differences over other portions, for example over the winding insulation and from the surface to the air gap, have to be kept as small as possible by means of a suitable design.
More common is a direct ventilation of the rotor via cooling channels which extend along the machine axis and have openings to the winding elements and to the air gap. Usually a cooling surface has to be formed via the winding in the grooves which requires considerable effort during the production of the coils.
Partial laminated stacks with in each case ventilation slots located therebetween are formed only in machines where the cores in the rotor are designed as laminations. As a result, a very large cooling surface is formed and the paths between the heat sources and the cooling surface are particularly short. In rotors of solid design, this cooling variant is not used due to mechanical and technological boundary conditions.